We have been successful in rendering enzymes nonimmunogenic by a chemical means. We propose to carry out comprehensive chemical, biochemical, immunological and pathological studies related to the therapeutic use of nonimmunogenic enzymes by intravenous injection. We will modify a number of enzymes by our procedure and evaluate in experimental animals (a) their loss of antigenicity, (b) their circulating life in the blood, (c) changes in the blood, (d) their eventual fate, (e) any pathological effects of enzyme administration. The following enzymes will be modified and tested: (a) asparaginases from various sources (for control of certain leukemias), (b) lysozymes from several sources (of potential value in bacterial infections of blood), (c) streptokinase and trypsin (blood clots), (d) uricase from Candida albicans, both for lowering blood uric acid levels and for possible injection at sites of tophi formation. The unique properties of the modified enzymes will be compared and contrasted with the native enzymes.